I don't think there is enough information to conclusively answer the question. The front page post says "Users on the 250 MB service plan can also select to automatically boost their plan to unlimited service once they reach their limit." which I think could be taken to either mean a temporary boost for just this month or a permanent switch to the unlimited plan.
The article also says that you will get alerts at 20%, 10% and 0% data left. I would hope that most people are able to take the hint and upgrade manually if they have to.
The article also says that you will get alerts at 20%, 10% and 0% data left. I would hope that most people are able to take the hint and upgrade manually if they have to.